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    <div class="sect1" lang="en" xml:lang="en">
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            <h2 class="title" style="clear: both"><a id="envlog_set_config"></a>DbEnv::log_set_config()</h2>
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      <pre class="programlisting">#include &lt;db_cxx.h&gt;

int
DbEnv::log_set_config(u_int32_t flags, int onoff); </pre>
      <p>
        The <code class="methodname">DbEnv::log_set_config()</code> method
        configures the Berkeley DB logging subsystem.
    </p>
      <p>
        The <code class="methodname">DbEnv::log_set_config()</code> method
        configures a database environment, not only operations performed
        using the specified <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a>  handle.
    </p>
      <p>
        The <code class="methodname">DbEnv::log_set_config()</code> method may be
        called at any time during the life of the application.
    </p>
      <p>
        The <code class="methodname">DbEnv::log_set_config()</code> <span>
            
            <span>
                method either returns a non-zero error value or throws an
                exception that encapsulates a non-zero error value on
                failure, and returns 0 on success.
            </span>
        </span>
    </p>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="idm139670058691968"></a>Parameters</h3>
            </div>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idm139670058690400"></a>flags</h4>
              </div>
            </div>
          </div>
          <p>
                The <span class="bold"><strong>flags</strong></span> parameter must
                be set by bitwise inclusively 
                <span class="bold"><strong>OR</strong></span>'ing together one or
                more of the following values:
            </p>
          <div class="itemizedlist">
            <ul type="disc">
              <li>
                <p><a id="log_set_config_DB_LOG_AUTO_REMOVE"></a>
                        <code class="literal">DB_LOG_AUTO_REMOVE</code>
                    </p>
                <p>
                        If set, Berkeley DB will automatically remove log
                        files that are no longer needed.
                    </p>
                <p>
                        Automatic log file removal is likely to make
                        catastrophic recovery impossible.
                    </p>
                <p>
                        Replication Manager applications operate in a
                        group-aware manner for log file removal, and
                        automatic log file removal simplifies the
                        application.
                    </p>
                <p>
                        Replication Base API applications will rarely want
                        to configure automatic log file removal as it
                        increases the likelihood a master will be unable to
                        satisfy a client's request for a recent log record.
                    </p>
                <p>
                        Calling
                        <code class="methodname">DbEnv::log_set_config()</code>
                        with the <code class="literal">DB_LOG_AUTO_REMOVE</code> flag
                        affects the database environment, including all
                        threads of control accessing the database
                        environment.
                    </p>
                <p>
                        The <code class="literal">DB_LOG_AUTO_REMOVE</code> flag may
                        be used to configure Berkeley DB at any time during
                        the life of the application.
                    </p>
              </li>
              <li>
                <p><a id="log_set_config_DB_LOG_BLOB"></a>
                        <code class="literal">DB_LOG_EXT_FILE</code>
                    </p>
                <p>
                        Enables full logging of 
                        <a class="link" href="blob.html" title="Chapter 14.  External Files">external file</a> data. Only
                        use this flag if using replication or running a hot
                        backup; otherwise, it will impose a performance
                        penalty on external file operations.
                    </p>
                <p>
                        This flag is off by default, unless Replication is
                        enabled for the environment. In that case, it is
                        on by default.
                    </p>
                <p>
                        The <code class="literal">DB_LOG_EXT_FILE</code> flag may be
                        used to configure Berkeley DB at any time during
                        the life of the application.
                    </p>
              </li>
              <li>
                <p><a id="log_set_config_DB_LOG_DIRECT"></a>
                        <code class="literal">DB_LOG_DIRECT</code>
                    </p>
                <p>
                        Turn off system buffering of Berkeley DB log files
                        to avoid double caching.
                    </p>
                <p>
                        Calling
                        <code class="methodname">DbEnv::log_set_config()</code>
                        with the DB_LOG_DIRECT flag only affects the
                        specified <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a>
                        handle (and any other Berkeley DB handles opened
                        within the scope of that handle). For consistent
                        behavior across the environment, all 
                        <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a>  handles
                        opened in the environment must either set the
                        DB_LOG_DIRECT flag or the flag should be specified
                        in the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> configuration file.
                    </p>
                <p>
                        The <code class="literal">DB_LOG_DIRECT</code> flag may be
                        used to configure Berkeley DB at any time during
                        the life of the application.
                    </p>
              </li>
              <li>
                <p><a id="log_set_config_DB_LOG_DSYNC"></a>
                          <code class="literal">DB_LOG_DSYNC</code>
                     </p>
                <p>
                         Configure Berkeley DB to flush log writes to the backing disk before
                         returning from the write system call, rather than flushing log writes
                         explicitly in a separate system call, as necessary.  This is only
                         available on some systems (for example, systems supporting the
                         IEEE/ANSI Std 1003.1 (POSIX) standard O_DSYNC flag, or systems
                         supporting the Windows FILE_FLAG_WRITE_THROUGH flag).  This flag may
                         result in inaccurate file modification times and other file-level
                         information for Berkeley DB log files.  This flag may offer a
                         performance increase on some systems and a performance decrease on
                         others.
                     </p>
                <p>
                         Calling
                         <code class="methodname">DbEnv::log_set_config()</code>
                         with the DB_LOG_DSYNC flag only affects the
                         specified <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a>
                         handle (and any other Berkeley DB handles opened
                         within the scope of that handle). For consistent
                         behavior across the environment, all 
                         <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a>  handles
                         opened in the environment must either set the
                         DB_LOG_DSYNC flag or the flag should be specified
                         in the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> configuration file.
                     </p>
                <p>
                        The <code class="literal">DB_LOG_DSYNC</code> flag may be
                        used to configure Berkeley DB at any time during
                        the life of the application.
                     </p>
              </li>
              <li>
                <p><a id="log_set_config_DB_LOG_IN_MEMORY"></a>
                        <code class="literal">DB_LOG_IN_MEMORY</code>
                    </p>
                <p>
                        If set, maintain transaction logs in memory rather
                        than on disk.  This means that transactions exhibit
                        the ACI (atomicity, consistency, and isolation)
                        properties, but not D (durability); that is,
                        database integrity will be maintained, but if the
                        application or system fails, integrity will not
                        persist.  All database files must be verified
                        and/or restored from a replication group master or
                        archival backup after application or system
                        failure.
                    </p>
                <p>
                        When in-memory logs are configured and no more log
                        buffer space is available, Berkeley DB methods may
                        return an additional error value,
                        <code class="literal">DB_LOG_BUFFER_FULL</code>.  When
                        choosing log buffer and file sizes for in-memory
                        logs, applications should ensure the in-memory log
                        buffer size is large enough that no transaction
                        will ever span the entire buffer, and avoid a state
                        where the in-memory buffer is full and no space can
                        be freed because a transaction that started in the
                        first log "file" is still active.
                    </p>
                <p>
                        Calling
                        <code class="methodname">DbEnv::log_set_config()</code>
                        with the <code class="literal">DB_LOG_IN_MEMORY</code> flag
                        affects the database environment, including all
                        threads of control accessing the database
                        environment.
                    </p>
                <p>
                        The <code class="literal">DB_LOG_IN_MEMORY</code> flag may be
                        used to configure Berkeley DB only before the 
                        <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>
                        method is called.
                    </p>
              </li>
              <li>
                <p><a id="log_set_config_DB_LOG_NOSYNC"></a>
                        <code class="literal">DB_LOG_NOSYNC</code>
                    </p>
                <p>
                        If set, the transaction log is not flushed from the
                        operating system cache to stable storage when a
                        transaction commits or the logging system switches
                        log files.  This can further increase performance
                        when all of the applications in an environment use
                        less-than-durable transactions (DB_TXN_NOSYNC and
                        DB_TXN_WRITE_NOSYNC).
                    </p>
                <p>
                        Turning on <code class="literal">DB_LOG_NOSYNC</code> removes
                        the durability guarantee of current or future
                        DB_TXN_SYNC transactions, as well as any
                        transactions which have been active since the last
                        checkpoint.  All database files must be verified
                        and/or restored from a replication group master or
                        archival backup after system failure.
                    </p>
                <p>
                        Turning off <code class="literal">DB_LOG_NOSYNC</code> may be
                        done at any time.  Current and future DB
                        DB_TXN_SYNC transactions will return to full ACID
                        characteristics once a checkpoint or log file
                        switch occurs.
                    </p>
                <p>
                        Calling
                        <code class="methodname">DbEnv::log_set_config()</code>
                        with the <code class="literal">DB_LOG_NOSYNC</code> flag
                        affects the database environment, including all
                        threads of control accessing the database
                        environment.
                    </p>
                <p>
                        The <code class="literal">DB_LOG_NOSYNC</code> flag may be
                        used to configure Berkeley DB at any time.  
                        <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>
                        method is called.
                    </p>
              </li>
              <li>
                <p>
                        <code class="literal">DB_LOG_ZERO</code>
                    </p>
                <p>
                        If set, zero all pages of a log file when that log
                        file is created.  This has shown to provide greater
                        transaction throughput in some environments. The
                        log file will be zeroed by the thread which needs
                        to re-create the new log file.  Other threads may
                        not write to the log file while this is happening.
                    </p>
                <p>
                        Calling
                        <code class="methodname">DbEnv::log_set_config()</code>
                        with the <code class="literal">DB_LOG_ZERO</code> flag
                        affects only the current environment handle.
                    </p>
                <p>
                        The <code class="literal">DB_LOG_ZERO</code> flag may be used
                        to configure Berkeley DB at any time.
                    </p>
              </li>
            </ul>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idm139670058646864"></a>onoff</h4>
              </div>
            </div>
          </div>
          <p>
                If the <span class="bold"><strong>onoff</strong></span> parameter is
                zero, the specified flags are cleared; otherwise they are
                set.
            </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="idm139670058697008"></a>Errors</h3>
            </div>
          </div>
        </div>
        <p>
             The <code class="methodname">DbEnv::log_set_config()</code> <span>
            
            <span>
                method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> 
                exception, encapsulating one of the following non-zero errors, or return one
                of the following non-zero errors:
            </span>
        </span>
        </p>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idm139670058650688"></a>EINVAL</h4>
              </div>
            </div>
          </div>
          <p>
                An invalid flag value or parameter was specified.
            </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="idm139670058663136"></a>Class</h3>
            </div>
          </div>
        </div>
        <p>
            <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a>  
        </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="idm139670058636688"></a>See Also</h3>
            </div>
          </div>
        </div>
        <p>
             <a class="xref" href="lsn.html#loglist" title="Logging Subsystem and Related Methods">Logging Subsystem and Related Methods</a> 
        </p>
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